Nonpatent Literature 1:
http://cp.literature.agilent.com/litweb/pdf/5965-7160J.pdf
An in-vehicle communication system is known which connects several devices using a single common wire harness (i.e., transmission line) in order to reduce the total weight of wire harnesses, without using conventional multiple wire harnesses. The communication system achieves the data transmission with proper timing to prevent the several devices from transmitting simultaneously, thereby permitting the use of a common transmission line and reducing the number of wire harnesses.
From another standpoint, such a communication system may undesirably have a specific frequency component. For example, input capacitances of devices or branching portions of the transmission line may pose variation in a characteristic impedance of the transmission line; the variation may cause a frequency characteristic to decrease a transmission power rapidly around a specific frequency. In addition, the increase of the specific frequency component may affect other devices such as an AM radio receiver not belonging to the communication system.
Further, Nonpatent Literature 1 discloses a configuration to perform a frequency conversion of digital data using an analog circuit such as a mixer, and transmit the data as radio waves.
However, the configuration in Nonpatent Literature 1 generally uses many analog circuits such as a mixer; this may pose difficulty in designing, increase the sizes of circuits, or reduce noise tolerance.